tut3.ashx - Tutorial 3 Q1. A receiving system employs an...

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Tutorial 3 Q1. A receiving system employs an antenna with a noise temperature of 40 K which is connected to a parametric amplifier through a waveguide with 1.6 dB loss. The parametric amplifier has a gain of 16 dB and a noise temperature of 60 K. The amplified output is connected to a TWT amplifier with a gain of 23 dB and a noise figure of 6 dB. The output of the TWT is connected to a mixer with a noise figure of 13 dB. Calculate the effective noise temperature: (a) at the antenna terminals with the antenna disconnected' (b) at the input terminals of the parametric amplifier. The standard temperature is 290 K. Solution: LO T a =40 K Feedline L 1 =1.6 dB Parametric amplifier G 2 =16 dB T 2 =60 K TWT amplifier G 3 =23 dB F 3 =6 dB Mixer F 4 =13 dB IF Antenna Feedline: Loss 1 1.6 dB 1.4454 L == Gain 1 1 11 1.4454 G L Effective noise temperature 0 (1 ) ( 1 . 4 4 5 4 1 ) 2 9 0 1 2 9 . 2 K TLT =- = - × = . Parametric amplifier: 2 16 dB 39.8 G 2 60 K T = TWT amplifier: 3 23 dB 199.5 G 3 6 dB 3.98 F 330 )8 6 4 . 2 K TFT Mixer: 4 13 dB 19.95 F 440 )5 4 9 6 . 3 K (a) Effective noise temperature 3 24 1 21 2 3 248.68 K e T TT GG G G =+ + + = . (b) Total effective noise temperature of the system 288.68 K sea TTT =+= Let e T be the equivalent effective noise temperature of the input of the parametric amplifier. Then 1234 234 () ( ) os e Nk T B G G G Gk T B G G G . 1 199.1 K es G ∴= = .
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Q2. A terrestrial microwave line-of-sight radio relay link is required between two points 40 km apart. (a) If each parabolic antenna has a diameter of 2 m and an aperture efficiency of 50%, while the operating noise figure of each receiving system is 13 dB, calculate the minimum carrier power required for the transmission of colour TV. Assume that the bandwidth of colour TV to be 10 MHz, and the signal-to-noise ratio for good quality reception to be 40 dB. (b) Given that the physical radius of the earth is 6400 km, calculate the height of the antenna above ground (assuming the antennas are of the same height) for satisfactory operation at 4 GHz. Solution: (a) Given 0.075 m λ= . 2 2 m 42 ee D A ππ = . 2 4 3509 e A G π == λ .
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tut3.ashx - Tutorial 3 Q1. A receiving system employs an...

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